324 PLA^'TiE NOV^E THURBERIAK-E. 



half an inch in diameter. There are sometimes one or two minute leaves near the base 

 of the scape-like peduncles ; otherwise these are entirely naked, slender, and 4 to 6 

 inches long. Head rather large for the size of the plant. Involucre somewhat cam- 

 panulate, 4 lines long, shorter than the disc ; the scales about 20, sparsely and mi- 

 nutely hirsute outside, thin, indistinctly 2 - 3-nerved, the inner ones with scarious mar- 

 gins, the exterior successively shorter and narroAver. Rays about 12; the ligules 3 or 

 4 lines long, oblong, tridenticulate at the apex, bright yellow. Tube of the disc-corol- 

 las longer than the throat and limb. Bristles of the pappus as delicate as in a Senecio, 

 but a little rigid, probably from being barbellate with strong denticulations, much as in 

 Arnica, but more sparsely so. — This little plant is excluded from the vast genus Sene- 

 cio by its imbricated involucre, and its scanty, uniserial, and barbellulate pappus ; from 

 Aronicum, by the uniserial pappus and the elongated branches of the style ; from Ar- 

 nica, by the alternate leaves and the whole character of the style ; and from all these 

 genera by its strongly convex or conical, tubercular-alveolate receptacle, and the flat 

 achenia (judging from the ovaries), fringed with strongly ciliate margins. — The genus 

 is dedicated, at Mr. Thurber's request, to John R Bartlett, Esq., the United States 

 Commissioner of the Boundary Survey at the time and under whose orders this collec- 

 tion was made, and the author of an elaborate work giving an account of this survey 

 and of the physical character, productions, antiquities, and ethnology of the regions 

 visited. 



Perezia Thurberi (sp. nov.) : glanduloso-puberula, subviscida ; caule herbaceo 1 - 

 3-pedali simplici crebe folioso ; foliis membranaceo-chartaceis ovato-oblongis oblongisve 

 basi cordata semi-amplexicaulibus scabrellis eximie reticulatis creberrime spinuloso- 

 denticulatis dentatisve, inferioribus obtusis, infimis fere obovatis, superioribus acutatis ; 

 corymbis polycephalis bracteatis in thyrsum demum oblongum digestis ; involucro 5 - 

 6-floro, squamis paucis triseriatis minute glandulosis omnibus acuminatis, extimis 

 subovatis, interioribus oblongis et lato-linearibus discum subsequantibus ; pappo albo, 

 setis rigidulis. — Rocky hills, near Santa Cruz, Sonora ; September, 1851. — " Viscid 

 and aromatic." Leaves crowded, 2\ to 4 inches long, the larger 2 inches wide, the 

 upper gradually reduced to subsagittate or lanceolate bracts. Heads crowded in a com- 

 pound corymb, or, in larger and fully developed specimens, forming an oblong and lax 

 thyrsus of six inches or more in length. Involucre 3 or 4 lines long, rather cylindrace- 

 ous than turbinate, of 9 or 10 cuspidate-acuminate scales. Corolla apparently purplish. 

 Achenia glandular. Pappus rather copious ; the bristles somewhat rigid, strongly sca- 

 brous, obscurely thickened at the apex. — This most resembles some states of P. 



